We've covered this before in earlier threads (which I'm too lazy to dig out). The national traffic law does not forbid motorcycles on expressways. The master list of questions for the motorcycle examination does refer to special restrictions: riding two-up is not allowed on the expressways and motorcycles are restricted to a maximum speed (which I think is 110kph). There is no national prohibition. But many provinces have local traditions that contravene the national law. I'm not sure where you'd find these written (except on the signs at expressway entrances) because I doubt that provinces have their own independent traffic laws (though I could be wrong on this).

That dodgy document appears to take its text from the national traffic law and/or the national drivers license examinations. You can buy these in any Xinhua book store.

But that does not mean the tolltaker or cop who has stopped you will relent when you whip out the law. Since when is China ruled by laws?

cheers